destroy --purge: also wipe agent state dirs

new --purge flag on the destroy verb (cli + admin socket + dashboard).
default destroy still keeps /var/lib/hyperhive/{agents,applied}/<name>/
so recreating with the same name reuses prior config + creds.
with --purge, both dirs go too (config history, claude creds, /state/
notes). no undo. dashboard adds a separate PURG3 button with an
explicit confirmation copy; the existing DESTR0Y button keeps the
soft semantics.

claude.md dashboard-action-surface section updated; todo entry
dropped.

hive-c0re/src/server.rs

@@ -115,8 +115,8 @@ async fn dispatch(req: &HostRequest, coord: Arc<Coordinator>) -> HostResponse {
                 });
                 HostResponse::success()
             }
-            HostRequest::Destroy { name } => {
-                actions::destroy(&coord, name).await?;
+            HostRequest::Destroy { name, purge } => {
+                actions::destroy(&coord, name, *purge).await?;
                 HostResponse::success()
             }
             HostRequest::Rebuild { name } => {